The Phase II Murchison Widefield Array: Design overview

We describe the motivation and design details of the "Phase II" upgrade of the Murchison Widefield Array(MWA) radio telescope. The expansion doubles to 256 the number of antenna tilesdeployed in the array. The new antenna tilesenhance the capabilities of the MWA in several key science areas. Seventy-two of the new tilesare deployed in a regular configuration near the existing MWA core. These new tilesenhance the surface brightnesssensitivity of the MWA and will improve the ability of the MWA to estimate the slope of the Epoch of Reionisation power spectrum by a factor of ~3.5. The remaining 56 tilesare deployed on long baselines, doubling the maximum baseline of the array and improving the array u,v coverage. The improved imaging capabilities will provide an order of magnitude improvement in the noise floorof MWA continuum images. The upgrade retains all of the features that have underpinned the MWA's success (large field-of-view, snapshot image quality, pointing agility) and boosts the scientific potential with enhanced imaging capabilities and by enabling new calibration strategies.